Method of absorption-desorption of hydrogen storage alloy and hydrogen storage alloy and fuel cell using said method

Abstract

According to the invention, hydrogen absorbed in a PCT curve low pressure region not desorbed and utilized so far can be desorbed easily by controlling a hydrogen storage alloy temperature in the final stage of a hydrogen desorption process (T2) to a temperature higher than the hydrogen storage alloy temperature in the hydrogen absorption process (T0) and a hydrogen storage alloy temperature in the initial stage of the hydrogen desorption process (T1) (T2>T1≧T0).

1 . A hydrogen absorption and desorption method for a hydrogen storage alloy which comprises steps of absorbing and desorbing hydrogen by properly repeating hydrogen pressurization and depressurization to said hydrogen storage alloy being a body-centered cubic hydrogen storage alloy having two-stage plateau characteristics or inclined plateau characteristics wherein a hydrogen storage alloy temperature in the final stage of hydrogen desorption process (T2) is controlled to a temperature higher than a hydrogen storage alloy temperature in a hydrogen absorption process (T0) and a hydrogen storage alloy temperature in the initial stage of the hydrogen desorption process (T1) (T2>T1≧T0).  
     
     
         2 . The hydrogen absorption and desorption method according to  claim 1 , wherein the hydrogen storage alloy temperature in the final stage of the hydrogen desorption process (T2) is 150° C. or lower.  
     
     
         3 . The hydrogen absorption and desorption method according to  claim 1  or  2 , wherein the process at or after the instance where hydrogen in the hydrogen storage alloy is decreased to any residual amount of 50% or less in the hydrogen desorption process is defined as the final stage for the hydrogen desorption process.  
     
     
         4 . The hydrogen absorption and desorption method according to any of  claims 1  to  3 , wherein the process at or after the instance where hydrogen in the hydrogen storage alloy is decreased to any residual amount of 25% or less in the hydrogen desorption process is defined as the final stage for the hydrogen desorption process.  
     
     
         5 . A body-centered cubic hydrogen storage alloy for conducting absorption and desorption of hydrogen in the reaction between the hydrogen storage alloy and hydrogen in which a hydrogen storage alloy temperature in the final stage of a hydrogen desorption process (T2) is controlled to a temperature higher than a hydrogen storage alloy temperature in the hydrogen absorption process (T0) and higher than a hydrogen storage alloy temperature in the initial stage of hydrogen desorption (T1) (T2>T1≧T0) wherein the hydrogen storage alloy has two-stage plateau characteristics or inclined plateau characteristics.  
     
     
         6 . The hydrogen storage alloy according to  claim 5  wherein said hydrogen storage alloy has a composition represented by the general formula: Ti X Cr Y M Z  in which M is one or more members selected from elements belonging to the groups IIa, IIIa, IVa, Va, VIa, VIIa, VIII, IIIb, and IVb of the periodical table, 20≦X+Y<100 atomic %, 0.5≦Y/X≦2, 0<Z≦80 atomic %, and includes inevitably intruded oxygen or nitrogen and minimum spinodal decomposition phase formed inevitably.  
     
     
         7 . The hydrogen storage alloy according to  claim 6 , wherein the additive element M is V at 60 atomic % or less.  
     
     
         8 . The hydrogen storage alloy according to  claim 6  or  7 , wherein the additive element M is one or more members selected from Mo, Al, Mn and rare earth elements at 10 atomic % or less.  
     
     
         9 . A fuel cell comprising a hydrogen storage tank incorporating a hydrogen storage alloy, a temperature control device for elevating or cooling a temperature directly of the hydrogen storage alloy or an atmospheric temperature of the absorption alloy, a fuel cell capable of outputting electric power by chemical change of hydrogen supplied from the hydrogen storage tank, and a control section for conducting control that a hydrogen storage alloy temperature in the final stage of a hydrogen desorption process (T2) is at a temperature higher than a hydrogen storage alloy temperature in a hydrogen absorption process (T0) and a hydrogen storage alloy temperature in the initial stage of the hydrogen desorption process (T1) (T2>T1≧T0).  
     
     
         10 . The fuel cell according to  claim 9 , wherein the control section is adapted to properly control the pressure, temperature and flow rate of the hydrogen gas supplied to the hydrogen storage tank and the fuel cell.  
     
     
         11 . The fuel cell according to  claim 9  or  10 , wherein the temperature control device can utilize a heat dissipated from the fuel cell or a heat of exhaust gases exhausted from the fuel cell for the temperature elevation.